write to a text file from HTML form using PHP

In addition to what Andy G said about changing the name of submit button:

<?php
//Get the email from POST
$email = $_REQUEST['email'];
$file = fopen("emaillist.txt","a+");
fwrite($file,$email);
print_r(error_get_last());

//redirect
header("Location: http://www.example.com/");

Don't leave any blank lines between <?php and the beginning of the file, otherwise redirect won't work.

In php theres an array called $_POST that stores all of the variables from a form when you post it. So $email would be found in $_POST['email']

The submission results will be stored in the $_POST variable:

<?php

$file = fopen("emaillist.txt","a+");

$email = $_POST['email']; 

fwrite($file,$email);
fclose($file); 
print_r(error_get_last());

?>

You have a few things you'll need to update here:

Form elements need to have different names, so you can differentiate between them in the PHP server-side code. Something like this:

<form action="emaillist.php" method="post">
    <input type="text" name="email" />
    <br />
    <br />
    <input type="submit" name="emailSubmit" value="submit" />
    <br />
</form>

You need to wrap your server-side code in a conditional to make sure it's a form post. Currently, when you first load this page, it's going to write to the file. But there's no content until you post back to the page again with the form data. So you need to check if it's a form post. A common way to do this is to check for the presence of the submit button in the post data:

if (isset($_POST["emailSubmit"])) {
    $file = fopen("emaillist.txt","a+");
    fwrite($file,$email);
    fclose($file); 
    print_r(error_get_last());
}

Just to confirm, since you say you're new to PHP... You're expecting the file to be written on the server and not on the client, correct?

To redirect to another page, you can simply set the location header in the server-side PHP code. This needs to be done before any content is emitted to the client. Since you only want this to happen on a post event, it should be in the same conditional as before:

if (isset($_POST["emailSubmit"])) {
    $file = fopen("emaillist.txt","a+");
    fwrite($file,$email);
    fclose($file); 
    print_r(error_get_last());

    header("Location: http://www.yoursite.com/newPage.php") ;
}

Try this, Use different name for submit button also check if the submit button was pressed than write to file. You also didn't get the posted email values

<?php
if(isset($_POST['submit']))
{
    $email = $_POST['email'];
    $file = fopen("emaillist.txt","a+");
    fwrite($file,$email);
    fclose($file); 
    print_r(error_get_last());
}
?>
<form action= "" method="post" name="form">
<input type="text" name="email">
<br>
<br>
<input type="submit" name="submit" value="submit"><br>
</form>

<?php
if (isset($_POST['emailSubmit'])) {
    $file = fopen('emaillist.txt','a+');
    $email = $_POST['nail'];
    $fmail = $email.PHP_EOL;
    fwrite($file,$fmail);
    fclose($file); 
    print_r(error_get_last());

    header("Location: http://www.yourdomain.com/thanks.html") ;
}

?>
<form action='emaillist.php' method='post'>
    <input type='text' name ='nail' size= '30'/>
    <br />
    <br />
    <input type='submit' name='emailSubmit' value='OK'/>
    <br />
</form>

Your submit button and input element and the form, have the same name "email". The first thing to do is to give them different names.

The name of the form also includes an extra space "email ".